The invention relates to a fluid actuating device for an electric switching apparatus such as a circuit breaker, particularly, a high-voltage power circuit breaker. The device of the invention includes an actuator arrangement which includes a differential piston and a cylinder. The actuator arrangement can be acted upon by pressure fluid through a main-valve arrangement with a control valve arrangement controlling the main-valve arrangement.
In a hydraulic actuating device of this kind the problem occurs of transmitting the closing and opening commands to the movable contacts of the electric circuit breaker with the least possible delay.
Accordingly, it is an object of the invention to prevent a creeping switching motion of the circuit breaker. Such a creeping switching motion can occur if the pressure of the pressure fluid drops so far that spring-loaded main-valves of the known arrangements are brought by their spring force into a position which leads to a reversal of the drive, so that, when the hydraulic pump starts up, the pumping rate directly determines the reversal speed of the movable contacts. Accordingly, and subsidiary to the foregoing object, it is another object of the invention to provide a fluid actuating device wherein the need for such spring-loaded main-valves is unnecessary.